RMW registers are registers with internal logic circuitry useable to provide a convenient way of directly changing the state of one or more bits in the register without affecting the other bits in the register. Data can be written directly to the register in one of various operating modes including: (i) an overwrite mode in which existing bit values are overwritten; (ii) a set mode in which selected bits are set while other bits are left unchanged, according to the data written; and (iii) a clear mode in which selected bits are cleared (reset) while leaving other bits unchanged, according to the data written. RMW registers find use in processor controlled systems, especially, module resets, interrupt enables, power enables, and input/output interfaces, providing bit-addressable modification (set/clear) functionality at the register to reduce processing burden at the processor, and to reduce traffic on shared busses.
A conventional RMW register includes dedicated logic circuitry for implementing the bit-modification functionality internally within the register. However, such logic circuitry increases the physical size of the register significantly. Where multiple RMW registers are used in an integrated circuit, a large amount of die area is consumed. Especially, when compared to the area occupied for simpler registers without built in bit-modification functionality.